High-temperature and high-pressure densities of aqueous NaClO4 solutions

Densities of four aqueous NaClO4 solutions (0.0825, 0.288, 0.488, 0.965 mol kg(-1) H2O) have been measured in the liquid phase with a constant-volume piezometer immersed in a precision liquid thermostat. Measurements were made at ten isotherms between 293 K and 573 K. The range of pressures was 0.1 to 38 MPa. The total uncertainties of density, pressure, temperature, and concentration measurements were estimated to be less than 0.06%, 0.05%, 15 mK, and 0.014%, respectively. Values of saturated densities were determined by extrapolating experimental P-p data to the vapor pressure at fixed temperature and composition. Partial and apparent molar volumes were derived by using measured values of density for the solutions and for pure water. The apparent molar volumes were extrapolated to zero concentration to yield partial molar volumes at infinite dilution. The temperature, pressure, and concentration dependences of partial and apparent molar volumes were studied. A polynomial type of equation of state for specific volume was obtained from the experimental data by a least-squares method as a function of temperature, pressure, and composition. The average absolute deviation between measured values and values calculated with this polynomial equation for density is 0.02%. The measured values of density, and apparent and partial molar volume are compared with data reported in the literature.